ABSTRACT
Wireless sensors which have more advantages relative to wired sensors are playing an important role in improving the quality of life in daily indoor space. The applications include home security systems for improving the safety of our home and vital-signs monitoring systems for improving our health. The sensor systems can remotely detect the echo reflected from a person and then estimate the state and/or vital signs such as respiration rate and heart rate, for example. Several types of wireless sensor device have thus far been developed such as video camera, passive infrared (IR), and microwave. The video camera is unacceptable for some applications from a privacy protection point of view, although it can monitor a wide area of the indoor space. Passive IR sensors are generally developed to be dedicated to a relatively small area such as the home entrance and toilet area. Microwave sensors such as the Doppler and the frequency-modulated continuous-wave (FM-CW) sensor, which are capable of penetrating a variety of nonmetallic materials such as inner walls, provide a wider coverage area when compared with video cameras and IR but are susceptible to interference from other wireless radio systems, thereby causing false alarms or false detection. Ultrawideband impulse radio (UWB-IR) has lately attracted considerable attention in short-range remote-sensor applications since it offers high ranging accuracy, multipath reduction, and environmental friendliness due to the very low energy emission [1-4]. However, it requires a very high-speed analog-to-digital conversion (ADC) and high-level processors in order to synchronize and detect the received nanosecond pulse. It may also cause interference with existing or future wireless systems using the same or nearby bands because it occupies a bandwidth wider than 500 MHz. Therefore,
CONTENTS
7.1 Introduction ........................................................................................................................ 161 7.2 Stepped-Frequency Modulation Ultrawideband Scheme ............................................ 162
7.2.1 Ultrawideband Impulse Radio Sensor ............................................................... 162 7.2.2 Stepped-Frequency Modulation Ultrawideband Sensor ................................. 163 7.2.3 Detect-and-Avoid and Spectrum Hole Technique ............................................ 165
7.3 Detect-and-Avoid Technique ............................................................................................ 167 7.4 Patient Care Sensing and Monitoring System ............................................................... 168
7.4.1 Sensing and Monitoring Algorithm .................................................................... 168 7.4.2 Measurement Results ............................................................................................ 170
7.5 Conclusions ......................................................................................................................... 171 References ..................................................................................................................................... 172
the ultrawideband (UWB) device operated in the lower band of 850 MHz to 3.14 GHz is required to implement the detect-and-avoid (DAA) technique in many countries such as Europe, Korea, and Japan [5].
